A duplexer component, in particular an antenna duplexer, has a transmission path, in which transmission signals generated by a transmitter are forwarded to a terminal for connecting an antenna. Furthermore, the duplexer component comprises a reception path, in which reception signals are forwarded from the antenna to a receiver.
A surface acoustic wave filter can be arranged as a transmission filter in the transmission path. The surface acoustic wave filter in the transmission path can have an input terminal for applying a transmission signal and an output terminal for outputting an output signal that is forwarded to the antenna for emission. The transmission filter is intended to have a passband having a low insertion loss for frequencies of the transmission signal to be emitted. Outside the passband, the transmission filter is intended to have a stop band having a high insertion loss, in order that interference signals do not reach the antenna or the transmitter via the transmission path.
A surface acoustic wave filter can likewise be arranged as a reception filter in the reception path, the filter having a passband having a low insertion loss in the frequency range of the reception signals to be received by the antenna. Outside the passband, the reception filter is intended to have a stop band having a high insertion loss, since received signals having frequencies in the stop band are intended to be suppressed to the greatest possible extent by the reception filter. The surface acoustic wave filter in the reception path can have an input terminal for applying the signal received by the antenna and a first output terminal for outputting a first output signal and a second output terminal for outputting a second output signal. By means of an embodiment of this type, the reception filter can be operated in an asymmetrical (unbalanced or single-ended) manner at the input side and in a symmetrical (balanced) manner at the output side.
In the case of a duplexer component, the surface acoustic wave filters in the transmission and reception paths can be embodied in such a way that the passband of the reception filter is spaced apart from the passband of the transmission filter by a few MHz, for example, 20 MHz to 100 MHz. For symmetrically operated duplexer components having a large frequency separation between the passband in the transmission path and reception path, the suppression of a signal having frequencies in the passband of the transmission filter by the reception filter and the suppression of a signal having frequencies in the passband of the reception filter by the transmission filter are intended to be as high as possible. Furthermore, a high degree of isolation between transmission and reception paths is desired.
These requirements could be fulfilled to the greatest possible extent by means of a symmetrical arrangement of transducer structures of the surface acoustic wave filter in the reception path and of the surface acoustic wave filter in the transmission path. However, since the surface acoustic wave filler in the reception path is operated asymmetrically on the input side and symmetrically on the output side, the transducers of the surface acoustic wave filter in the reception path are arranged asymmetrically. On account of the asymmetrical orientation of the transducers, a phase difference of 180° can be obtained between the output signals at the first and second output terminals of the reception filter.
The asymmetrical arrangement of the transducer structures has the effect, however, that signals which are coupled into the reception path from the transmission filter, between the input side of the transmission filter and the first output terminal of the reception path, experience a different attenuation than those signals which are transferred between the input terminal of the transmission filter and the second output terminal of the reception filter. On account of this asymmetry, therefore, a non-uniform isolation occurs between the transmission path and the reception path.